syscall: let mkall.sh work on multiarch systems (like Precise)
syscall: let mkall.sh work on multiarch systems (like Precise)

R=golang-dev, rsc
CC=golang-dev
https://codereview.appspot.com/6912063

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang